1. Field of the Invention
The present invention relates generally to a commutator or position sensing apparatus utilizing magnetically sensitive elements. The present invention relates specifically to motor commutator assemblies sensing ring magnets which pass before packaged Hall sensing elements. The present invention may also be adapted to linear rather than rotary position sensing schemes.
2. Description of the Related Art
A commutator, for present purposes, is defined as an electrical device which takes the changing magnetic signals of an object to be sensed and converts them to electrical signals whereby the position of the target object can be known. As the need for ever increasing sensitivity of position sensing becomes finer, such as in control motor applications or automotive brake sensing systems, the need for accurate placement of Hall or other magnetic sensors becomes greater. Prepackaged Hall sensors, while economical, may not have placement accuracy to accomplish fine position control utilizing known systems.
In the past, commutator boards have located the prepackaged Hall sensors by aligning their plastic packages. However, the plastic package is located around the leadframe of the Hall element with less accuracy than that with which the Hall element is placed on an individual lead of the leadframe. Referencing FIG. 1, a prepackaged Hall sensor 11 will consist of the leadframe having three leads 13, 15, 17 on which is placed the magnetically sensitive Hall effect silicon die 19, usually on the center lead 15. The leadframe including the silicon 19 is then packaged for protection with plastic casing 21. However, the molding of the plastic casing is generally held to a much looser tolerances than the placement of the silicon die 19 on the leadframe. That is, the plastic package 21 may be skewed left or right or tilted so that the center of the package or plastic case 21 does not correspond with the true center position of the silicon die 19 on the leadframe as indicated by the dashed line 23.
However, most known position sensing assemblies using prepackaged Hall sensors locate the position of the Hall element according to the plastic case 21, when a positioning bracket is provided. If a positioning bracket is not provided, the prepackaged Hall sensors are located according to the hole placement on a printed circuit board (PCB) to which such sensors are mounted. However, this is an undesirable situation in that the Hall sensor packages themselves are exposed to misplacement through bumping, bending, or the like in any of a variety of orientations. Also, fixturing of the prepackaged Hall sensors to the PC board is problematic. Further, the known protective placement brackets do not orient the sensors in all axes sufficiently to provide ease of manufacturing assembly and reliable center-to-center distance of the Hall sensors.
It is therefore desirable that a bracket assembly be developed that accurately orients the silicon die of the Hall sensor with respect to each other in as many axes as possible while protecting the placement of the Hall sensors and providing for ease of manufacturability.